An electric power tool includes a motor with output just for that purpose and, if its own power supply is a detachable battery pack, is equipped with a battery pack for a voltage and a capacity corresponding to the motor output. Therefore, different electric power tools each require battery packs corresponding to their own voltages and capacitors.
Japanese Patent Application Publication Number 2002-027675 (hereinafter referred to as a “document 1”) discloses an electric power tool capable of being equipped with a battery pack, which is not just original one, of such different battery packs as long as satisfying a voltage condition.
When a rated output voltage of an original battery pack for an electric power tool is “A”, the tool shown in the document 1 can be equipped with a battery pack of which rated output voltage is equal to or less than “A”.
It is preferable from a safety point of view that a high order battery pack of which voltage is higher than that of an original battery pack cannot be equipped. However, it is impossible to respond to a request of use of such a high order battery pack just for a short time even if the high order battery pack is around when an original battery pack runs down.